The chemical element content of Red Blood Cells (bulk: C, Fe, P, and ionic: K, Na, Cl, Mg) will be measured by automated electron probe analysis, counting all these elements by the same method in the same individual RBC in large number. The mounting procedure will avoid ionic translocation by spraying the RBC until the hardware to analyze the cells kept frozen is fully developed. By inducing a reversible increase in monovalent cations permeability with nystatin treatment, it will be possible to obtain cells with standardized Na, K and Cl concentrations. Such cells will provide calibration curves to calculate Na, K and Cl concentration in individual normal cells. Absolute method of quantitation will provide the concentration of the elements measured in individual cells. Multiple correlation will be studied between all the chemical elements counted. Histograms of elemental content will be compared between elements for the same population of cells. For a given element, histograms will be systematically studied in human RBC in function of the age and sex of the donor and in function of the age of the RBC. The RBC will be analyzed maintained frozen hydrated at or closed liquid nitrogen temperature. Such analysis of frozen hydrated sample will reduce or eliminate ionic redistribution and contamination by the suspending medium. Frozen hydrated analysis will be possible by the development of a new electron probe with a special interlock chamber, specimen stage cooled with liquid nitrogen and a vaccum which is oil free. Other cell systems (mycoplasma, lymphocytes) will be studied.